I absolutely loved the premiere. There were 2 or 3 times when I rewound a scene just because I immediately wanted to see it again. An intensely beautiful and artistically exciting episode of television.
Then there is a precipitous decline. The problems are already clear in Episode 2 but become glaring in Episode 3, bleeding into 4.
The horror scenes still work, and some images are still brilliant and interesting. But the writing gets lazy. The early childhood flashbacks, for example, are little more than a collection of cliches. Frolicking in a field laughing (which we see so many times), mother marking his height on the door frame. Really, that's the best you can do?
The exposition gets very bad, too. Episode 4 has some of the worst. They basically do a record scratch and stop the episode to explain the Kerry/Cary thing. Then, in a scene a couple minutes later: "It still amazes me how she only ages when she's outside your body." I cringed so hard. What a dumb way to insert exposition. "It still amazes me how..."
Worst of all is Rachel Keller. Starting with Episode 2, this is a profoundly uninteresting performance of a profoundly uninteresting character. The magic from the premiere is just gone. Absent better writing, Rachel Keller is just not prepared to imbue the character with anything special. Her acting worked wonderfully in Fargo, because that character was so specific. Here, you can tell she's just playing a version of herself. It's like a normal person is awkwardly taking up space in these scenes. So dull and distracting — especially when she occupies so much screen time.
Still, I feel like I shouldn't take Legion for granted. I'm on Episode 4, so I'll guess I'll see if it rebounds.